In electrical discharge machining of the type described above, which is commonly called "sinking EDM", it has hitherto been necessary to prepare a tool electrode shaped with a desired contour to be complementarily reproduced in the workpiece. Thus, a conventional sinking-type EDM electrode may be a precision-machined conductive block or a sheet metal element precision-deformed or obtained on a precision-electroforming mold. The preparation of such a tool electrode, however, is generally time-consuming and/or entails considerable skill and labor and, as a consequence, may make a desired EDM job unduly costly or often impractical. Furthermore, an EDM electrode is subject to electroerosive wear and must be frequently replaced in a customary EDM operation and this requirement further adds to cost and labor.
These problems may be alleviated by an improved EDM tool electrode disclosed in U.S. Pat. No. 2,909,641 to KUCYN issued Oct. 20, 1959 wherein a multiplicity of conductive pins are stacked in side-by-side relationship to constitute the tool electrode whereby the end surfaces of the pin combine to establish a desired machining face for the electrode. Such a tool electrode, however, is only applicable to rough EDM operations and is incapable of yielding a satisfactory EDM surface finish, thus necessitating a laborious and time-consuming hand-finishing of the rough-machined surface.